1. Field of the Invention
This invention relates to creating a uniform texture on the face of an object. More particularly, the invention relates to an improved method and apparatus for abrasive blasting the face of an object to give it a desired uniform appearance.
2. Background Art
Abrasive blasting, commonly referred to as sandblasting, has been a method for cleaning and deburring objects for years. Recently, the concrete industry has given this technique increased attention for other purposes, namely, as a method to prepare attractive surfaces for use in the construction industry. An example is texturized concrete blocks.
An important consideration in preparing a texturized surface is that the treated face have a uniform appearance. There have been attempts to achieve this objective in the prior art, but the processes developed have been ineffective or wasteful. For example, construction of the airport in San Antonio, Tex. used concrete blocks that were individually blasted by operators. That is, an operator manually moved a sandblasting apparatus back and forth across the face of each concrete block before its installation. This method of texturing a surface is expensive because it is labor intensive. It also wastes materials since little, if any, sand can be reused. In addition, the results are not uniform from block to block. Variations result from differences that exist between individual operators as well as variances in each operator's actions from block to block.
Another technique to texturize the face of an object is taught in Balhorn, U.S. Pat. No. 4,897,969. Balhorn relies on an automated process in which the object to be sandblasted moves via a conveyor through a sandblasting spray. However, to prevent non-uniformity of the surface caused by the concentration of particles in the central local, Balhorn requires a baffle plate to block the concentrated particle region. The concentration of blast media decreases as the radial distance from the center of the spray effluent is increased. The baffle blocks the concentrated area of particulant in the central area and only allows a portion of the less concentrated effluent to spray the object. Balhorn teaches that the baffle which blocks the concentrated particulate spray aids in achieving a uniformly textured face.
Balhorn, however, has drawbacks. A high percentage of the blast media is wasted because the baffle blocks the concentrated spray from the central area of the nozzle and only allows periphery particles to contact the object. Additionally, the nozzle has to be placed at a considerable distance from the face of the object to achieve a uniform result. A distance of over five feet is common, but the area of uniformity is still restricted.